1. Field of Invention
The present invention relates to a projection display device having a control circuit substrate on which a control circuit is mounted for controlling driving of the device according to an input operation signal from an external apparatus connected to the device, and particularly to a projection display device having a structure in which a signal transmission element having an opposite light emitting element and light receiving element is provided in a passage for transmitting an external input signal to a control circuit on a control circuit substrate.
2. Description of Related Art
When a signal generated in a first circuit substrate is transmitted from the first circuit substrate to a second circuit substrate and decoded by signal decoding means arranged on the second circuit substrate, it is generally necessary to draw a wire cable such as a lead wire from the first circuit substrate to the second circuit substrate. Namely, communication between the circuit substrates is performed by using electric signals. In this case, where the distance between the first circuit substrate and the second circuit substrate is relatively long, or electrical noise occurs between the first circuit substrate and the second circuit substrate, means for intensifying electric signals or means for removing noise is required. Further, where the voltage of an electric signal handled in the first circuit substrate is different from that in the second circuit substrate, means for converting the voltage of an electric signal is required.
In a product such as a projection display device, in which various electric devices and optical systems are arranged in a compact device case, and many circuits are arranged for controlling driving of these devices, a plurality of circuit substrates must be arranged, thereby requiring signal transmission and reception between the circuit substrates. Conventionally, the circuit substrates are connected by cables so that such signal transmission and reception is carried out by using electric signals.
However, in realization of miniaturization of a product (device), miniaturization is difficult because a space is required for providing a connector for connecting cables and for drawing the cables between a first circuit substrate and a second circuit substrate, for example, in order to transmit a signal from the first circuit substrate to the second circuit substrate.
Where a relatively large electric noise occurs in the product, or a long cable must be used, it is necessary to arrange a transmission buffer on the first circuit substrate and a receiving buffer and means (noise filter) for removing noise on the second circuit substrate. Particularly, the projection display device has noise sources such as a light source lamp driven at a high voltage, and an image signal processing circuit for handling digital signals, and thus requires such buffers and noise removing means.
Furthermore, where the voltage of an electric signal handled by the first circuit substrate is different from that in the second circuit substrate, means for converting the voltage is also required.
Arrangement of the buffers, the noise removing means and the voltage converting means on the circuit substrates not only interferes with miniaturization of the product but also causes an increase in the product cost.
The present invention has been achieved in consideration of the above problem, and an object of the invention is to provide means for communication between circuit substrates, which permits miniaturization of a device and cost reduction.
In order to achieve the object, a projection display device of the present invention includes a light source; an optical system for optically processing the light emitted from the light source to form an optical image corresponding to image information; a projection lens for projecting the image formed by the optical system on a projection plane; a device case for containing at least the light source and the optical system; a control circuit substrate contained in a predetermined space in the device case, for mounting a control circuit for controlling drive of the device; an external apparatus connecting terminal provided on the control circuit substrate so that the control circuit is operated by an input operation signal from an external apparatus; and a signal transmission circuit including a light emitting element and a light receiving element and provided in an external input signal transmission passage between the terminal and the control circuit; the control circuit substrate including a first circuit substrate on which the control circuit and the light receiving element are provided, and a second circuit substrate which is arranged opposite to the first circuit substrate, and on which the external apparatus connecting terminal and the light emitting element are provided.
Since the control circuit substrate includes the first and second circuit substrates, a space for mounting electronic components on the control circuit substrate is extended.
Since the light emitting element and light receiving element serving as a signal transmission circuit are provided opposite to each other between the first and second circuit substrates, a space for mounting electronic components on each of the circuit substrates is also extended.
Since a plurality of circuit substrates are provided, various external apparatus connecting terminals can be provided on the circuit substrates. Also, since the external apparatus connecting terminal is provided on the second circuit substrate without the control circuit, many other external apparatus connecting terminals can be provided on the first circuit substrate.
Since a medium for communication from the first circuit substrate to the second circuit substrate comprises optical signals, there is no need for a space for providing a connector for connecting cables and drawing the cables between the first circuit substrate and the second circuit substrate, thereby permitting close arrangement of the first and second circuit substrates. In addition, since optical signals are not affected by noise sources such as a light source lamp driven at a high voltage and an image signal processing circuit, there is no need for a buffer and noise removing means, which are needed in a conventional device.
Even when the voltage of a signal handled by the first circuit substrate is different from that in the second circuit substrate, the voltage of a signal can be changed by using the light emitting element and the light receiving element having desired photoelectric conversion efficiency, and thus another voltage converting means need not be provided.
Therefore, the present invention causes extension of a space for mounting electronic components, and a decrease in a space for containing the control circuit substrate, thereby achieving high-density mounting and a compact device. Also, the degree of layout freedom for arrangement of other external apparatus connecting terminals is increased.
In the projection display device of the present invention, the first circuit substrate preferably comprises a main circuit substrate on which the control circuit is mounted, and a sub-circuit substrate electrically connected to the main circuit substrate, disposed between the main circuit substrate and the second circuit substrate, and provided with the light receiving element.
Since the control circuit substrate comprises the three circuit substrates, the space for mounting electronic parts is further extended, and more external apparatus connecting terminals can be provided on the circuit substrates.
Therefore, it is possible to achieve higher-density mounting or more compact control circuit substrate, that is, a more compact device.
In the projection display device of the present invention, the light receiving element is preferably provided on a side of the first circuit substrate which faces the second circuit substrate with the light receiving plane parallel to the first circuit substrate, and the light emitting element is preferably provided with a light emission portion opposite to a light receiving plane of the light receiving element.
The amount of projection (height) of the light emitting element and the light receiving element from the circuit substrates are smaller than those in a case where the light emitting element and light receiving element are provided in a standing condition on the circuit substrates. There is thus a lower possibility that the light emitting element and light receiving element contact other members or the like in the step of mounting other electronic components on the control circuit substrate and the step of assembling the control circuit substrate in the device case, thereby facilitating the step of mounting electronic components, and the step of assembling the control circuit substrate.
Where the light emitting element and the light receiving element are provided in a standing condition on the circuit substrates, the height of the light emitting element must be adjusted so that the light emission plane of the light emitting element coincides with the light receiving plane of the light receiving element, thereby causing difficulties in the work. Also, a spacer must be interposed in a leg (lead wire) of the light emitting element in order to adjust the height and prevent from falling of the light emitting element. However, since the light emitting element and light receiving element are respectively provided along the surfaces of the circuit substrates, there is no problem of requiring adjustment of the height of the light emitting element and the spacer, thereby simplifying the construction of the first circuit substrate.
In the projection display device of the present invention, the end of a lead wire led out of the light emission portion of the light emitting element is preferably mounted to the surface of the second circuit substrate, and the lead wire is preferably bent along the surface of the second circuit substrate.
By bending the lead wire, the light emission portion can be disposed in parallel with the second circuit substrate, and thus the spacer for supporting the lead wire need not be provided.
In the present invention, the light emission portion of the light emitting element is preferably provided so that at least the end thereof projects from the side edge of the second circuit substrate.
Since the light emitting element is mounted at a position near the side edge of the second circuit substrate, the space for mounting electronic components on the second circuit substrate is extended, thereby enabling high-density mounting of the control circuit substrate or achievement of a compact device. Since the light emitted from the light emitting element is not intercepted by the second circuit substrate, the light emitting element can be mounted on either of the surface and rear sides of the second circuit substrate.
In the projection display device of the present invention, a notch is preferably formed at a side edge of the second circuit substrate so that the light emitting element is provided with at least a portion of the light emission portion projecting into the notch.
Since the light emitting element is provided within the second circuit substrate (does not project outward from the second circuit substrate), the light emitting element is less likely to contact other members. In addition, since the light emitting element does not project outward from the second circuit substrate, the space for containing the second circuit substrate in the device can be narrowed in the length direction of the circuit substrate.
Therefore, the light emitting element does not project upward and outward from the second circuit substrate, thereby facilitating handling of the second circuit substrate, and narrowing the space for mounting the circuit substrate in the length direction of the circuit substrate, that is, making the device compact.
In the projection display device of the present invention, the light emitting element is preferably mounted on the surface side of the second circuit substrate which is opposite to the first circuit substrate.
The light emitting element can be soldered to the second circuit substrate by one time of solder flow together with other electronic components to be mounted on the second circuit substrate, thereby facilitating mounting of the light emitting element.
In the projection display device of the present invention, the light emitting element is preferably mounted on the surface side of the second circuit substrate, which faces the first circuit substrate.
Since the light emitting element is absent on the side of the second circuit substrate where electronic components are mounted, the space for mounting the electronic components on the second circuit substrate is extended. Also, the light emission portion of the light emitting element is located closer to the light receiving plane of the light receiving element than a case where the light emitting element is mounted on the electronic part mounting side of the second circuit substrate, thereby permitting correct transmission of external input signals.
Therefore, the electronic part mounting space on the second circuit substrate is extended, thereby permitting high-density mounting of the control circuit substrate or achievement of a compact device.
Since the light emission portion of the light emitting element is located closer to the light receiving plane of the light receiving element, thereby achieving correct transmission of external input signals.
In the projection display device of the present invention, the first circuit substrate is preferably arranged along the side wall of the device case, and the second circuit substrate is preferably arranged in a substantially triangular space formed between the optical system and the device case.
The substantially triangular space between the optical system and the device case in the device case can effectively be employed as a circuit substrate containing portion.
Therefore, the space in the device case is effectively utilized, thereby achieving a further compact device.